1. Field of the Invention
The present invention relates to an apparatus for connecting a bare semiconductor die having a size and bond pad arrangement, either solder ball arrangement, or pin arrangement (hereinafter referred to generally as a xe2x80x9cterminal arrangementxe2x80x9d), which does not conform to a printed circuit board with a specific or standardized pin out, connector pad, or lead placement (hereinafter referred to generally as a xe2x80x9cconnection arrangementxe2x80x9d). More particularly, the present invention relates to an intermediate conductor-carrying substrate (hereinafter referred to generally as an xe2x80x9cadaptor boardxe2x80x9d) for connecting a nonconforming bare die to another printed circuit board having a given connection arrangement (hereinafter referred to generally as a xe2x80x9cmaster boardxe2x80x9d).
2. State of the Art
Definitions: The following terms and acronyms will be used throughout the application and are defined as follows:
BGAxe2x80x94Ball Grid Array: An array of minute solder balls disposed on an attachment surface of a semiconductor die wherein the solder balls are refluxed for simultaneous attachment and electrical communication of the semiconductor die to a printed circuit board.
COBxe2x80x94Chip On Board: The techniques used to attach semiconductor dice to a printed circuit board, including flip chip attachment, wirebonding, and tape automated bonding (xe2x80x9cTABxe2x80x9d).
Flip Chip: A chip or die that has bumped terminations spaced around the active surface of the die and is intended for facedown mounting.
Flip Chip Attachment: A method of attaching a semiconductor die to a substrate in which the die is flipped so that the connecting conductor pads on the face of the die are set on mirror-image pads on the substrate (i.e. printed circuit board) and bonded by refluxing the solder.
Glob Top: A glob of encapsulant material (usually epoxy or silicone or a combination thereof) surrounding a semiconductor die in the COB assembly process.
PGAxe2x80x94Pin Grid Array: An array of small pins extending substantially perpendicularly from the major plane of a semiconductor die, wherein the pins conform to a specific arrangement on a printed circuit board for attachment thereto.
SLICCxe2x80x94Slightly Larger than Integrated Circuit Carrier: An array of minute solder balls disposed on an attachment surface of a semiconductor die similar to a BGA, but having a smaller solder ball pitch and diameter than a BGA.
State-of-the-art COB technology generally consists of three semiconductor dice to printed circuit boards attachment techniques: flip chip attachment, wirebonding, and TAB.
Flip chip attachment consists of attaching a semiconductor die, generally having a BGA, a SLICC or a PGA, to a printed circuit board. With the BGA or SLICC, the solder ball arrangement on the semiconductor die must be a mirror-image of the connecting bond pads on the printed circuit board such that precise connection is made. The semiconductor die is bonded to the printed circuit board by refluxing the solder balls. With the PGA, the pin arrangement of the semiconductor die must be a mirror-image of the pin recesses on the printed circuit board. After insertion, the semiconductor die is generally bonded by soldering the pins into place. An under-fill encapsulant is generally disposed between the semiconductor die and the printed circuit board to prevent contamination. A variation of the pin-in-recess PGA is a J-lead PGA, wherein the loops of the J""s are soldered to pads on the surface of the circuit board. Nonetheless, the lead and pad locations must coincide, as with the other referenced flip chip techniques.
Wirebonding and TAB attachment generally begins with attaching a semiconductor die to the surface of a printed circuit board with an appropriate adhesive. In wirebonding, a plurality of bond wires are attached, one at a time, from each bond pad on the semiconductor die and to a corresponding lead on the printed circuit board. The bond wires are generally attached through one of three industry-standard wirebonding techniques: ultrasonic bondingxe2x80x94using a combination of pressure and ultrasonic vibration bursts to form a metallurgical cold weld; thermocompression bondingxe2x80x94using a combination of pressure and elevated temperature to form a weld; and thermosonic bondingxe2x80x94using a combination of pressure, elevated temperature, and ultrasonic vibration bursts. The die may be oriented either face up or face down (with its active surface and bond pads either up or down with respect to the circuit board) for wire bonding, although face up orientation is more common. With TAB, metal tape leads are attached between the bond pads on the semiconductor die and the leads on the printed circuit board. An encapsulant is generally used to cover the bond wires and metal tape leads to prevent contamination.
Although the foregoing methods are effective for bonding semiconductor dice to printed circuit boards, the terminal arrangements of the dice and the connection arrangements of the boards must be designed to accommodate one another. Thus, it may be impossible to electrically connect a particular semiconductor die to a printed circuit board for which the semiconductor die terminal arrangement was not designed to match the board""s connection arrangement. With either wirebond or TAB attachment, the semiconductor die bond pad may not correspond to the lead ends on the circuit board, and thus attachment is either impossible or extremely difficult due to the need for overlong wires and the potential for inter-wire contact and shorting. With flip chip attachment, if the printed circuit board connection arrangement is not a mirror-image of the solder ball or pin arrangement (terminal arrangement) on the semiconductor die, electrically connecting the flip chip to the printed circuit board is impossible.
Therefore, it would be advantageous to develop an apparatus for connecting a semiconductor die having a size and bond pad arrangement, solder ball arrangement, or pin arrangement (xe2x80x9cI/O patternxe2x80x9d) which does not conform to a printed circuit board with a specific or standardized pin out, connection pad location, or lead placement (xe2x80x9cI/O patternxe2x80x9d).
The present invention relates to an intermediate printed circuit board or other conductor-carrying substrate that functions as an adaptor board for electrically connecting one or more bare semiconductor dice of a variety of sizes and bond pad locations, solder ball arrangement, or pin arrangement, to a master printed circuit board with a specific or standardized pin out, connector pad location, or lead placement.
An adaptor printed circuit board or substrate (xe2x80x9cadaptor boardxe2x80x9d) is sized and configured with an I/O pattern to accommodate its attachment to the master printed circuit board (xe2x80x9cmaster boardxe2x80x9d). If the master board is configured to receive a specific pin out or specific connector pad locations, the adaptor board is configured on its master board attachment surface with pins or solder balls in mirror-image to the master board connection arrangement to make electrical contact with the specific pin out or connector pads on the printed circuit board. If the master board is configured to receive a bond wire, the adaptor board is configured and sized to provide wire bond pads on its upper surface closely adjacent the bond pads of the master board leads. The adaptor board can, of course, be configured to accommodate other attachment and electrical connection means known in the industry, as well as other components in addition to the semiconductor die or dice carried thereon.
On the semiconductor die side of the adaptor board, one or more semiconductor dice are attached. If a xe2x80x9cflip chipxe2x80x9d die is attached to the adaptor board, the adaptor board will, of course, be configured with an I/O pattern to receive the flip chip with a specific pin out or connector pad locations. The pin out or connector pads on the adaptor board are connected to circuit traces on or through the adaptor board. The circuit traces form the electrical communication path from the pin recesses or connector pads on the adaptor board to the connection points to the master board.
If a xe2x80x9cleads overxe2x80x9d die is used with the adaptor board, the bond pads on the die are wirebonded to the adaptor board. Preferably, the leads over die are attached to the adaptor board with the bond pads facing the adaptor board. The bond wires are attached to the leads over die bond pads and extend into a via or vias in the adaptor board. The bond wires are attached to an I/O pattern of adaptor board bond pads within the via from which circuit traces extend, or to leads on the master board side of the adaptor board.
It is, of course, understood that the leads over die can be attached to the adaptor board with the bond pads facing away from the adaptor board. Thus, the bond wires are simply attached to the bond pads on the leads over die and to a corresponding I/O pattern of adaptor board pad on the semiconductor die side of the adaptor board.
Preferably, the exposed circuitry of the die and the die-to-adaptor board interconnection is sealed from contamination by a glob top after wire bonding or an underflow compound in the case of a flip chip attachment.
Furthermore, it is understood that with the use of wire bonds, the adaptor boards can be stacked on top of each other and connected to the adaptor board as by wire bonding.